Radiosynoviorthesis or radiation synovectomy is a form of treatment for recurrent synovitis that involves ablating the synovium by intra-articular administration of radionuclides. The purpose is to destroy the synovium before it can cause cartilage destruction and result in a chronic, debilitating arthropathy. This treatment was developed as an alternative or adjunct to surgical and chemical forms of synovectomy. Ansell et al. (1) were the first to publish their results in 1963, and Delbarre et al. (2) first coined the term “radiosynoviorthesis” to describe the treatment.